Christopher is 72 years old and Vanessa is 18 years old. How many years will it take until Christopher is only 3 times as old as Vanessa?
Answer: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Christopher will be $72 + y$ years old and Vanessa will be $18 + y$ years old. At that time, Christopher will be 3 times as old as Vanessa. Writing this information as an equation, we get: $72 + y = 3 (18 + y)$ Simplifying the right side of this equation, we get: $72 + y = 54 + 3 y$ Solving for $y$ , we get: $2 y = 18$ $y = 9$.